Moving picture video is typically recorded or encoded at a pre-determined frame rate. For example, cinema films are typically recorded at a fixed rate of 24 frames per second (fps). Video as broadcast for television in accordance with the NTSC standard, on the other hand, is encoded at 30 fps. Video broadcast in accordance with European PAL or SECAM standards is encoded at 25 fps.
Conversion between frame rates has created challenges. One common technique of converting frame rates involves dropping or repeating frames within a frame sequence. For example, telecine conversion (often referred to as 3:2 pull down) is used to convert 24 fps motion picture video to 60 fields per second (30 fps). Each second frame spans 3 fields, while each other second frame spans two fields. Telecine conversion is, for example, detailed in Charles Poynton, Digital Video and HDTV Algorithms and Interfaces, (San Francisco: Morgan Kaufmann Publishers, 2003), the contents of which are hereby incorporated by reference.
Various other techniques for frame rate conversion are discussed in John Watkinson “The Engineer's Guide to Standards Conversion”, Snell and Wilcox Handbook Series and “The Engineer's Guide to Motion Compensation”, Snell and Wilcox Handbook Series.
More recently, frame rate conversion has not only been used for conversion between standards, but also to enhance overall video quality. For example, in an effort to reduce perceptible flicker associate with conventional PAL televisions, high frame rate 100 fields per second (50 fps) televisions have become available.
In the future, higher frame rates may become a significant component in providing higher quality home video. Existing video, however, is not readily available at the higher frame rate. Accordingly, frame rate conversion will be necessary. Such conversion, in real time presents numerous challenges.
For example, if frame rate conversion introduces material delays, associated audio may no longer be synchronized with the video. Likewise, conversion may need to be performed on video sources that have already undergone telecine or other frame rate conversion.
Accordingly, there is a need for improved frame rate conversion techniques.